Hybrid high-k first and high-k last replacement gate process

ABSTRACT

An integrated circuit and method with a metal gate NMOS transistor with a high-k first gate dielectric on a high quality thermally grown interface dielectric and with a metal gate PMOS transistor with a high-k last gate dielectric on a chemically grown interface dielectric.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under U.S.C. §119(e) ofU.S. Provisional Application 61/921,495 (filed Dec. 29, 2013), thecontents of which are hereby incorporated by reference.

FIELD OF INVENTION

This invention relates to the field of integrated circuits. Moreparticularly, this invention relates to replacement gate transistors inintegrated circuits.

BACKGROUND

As the geometries for integrated circuits have scaled to smaller andsmaller dimensions, it has become necessary to replace polysilicontransistor gates with metal gates to enable scaling to continue tosmaller dimensions. When voltage is applied to a polysilicon gate, thepolysilicon grains next to the gate dielectric become depleted ofcarriers increasing the electrical thickness of the gate dielectric andexacerbating short channel effects. Metal gates do not deplete whenvoltage is applied to the metal gate.

Because the work function of p-channel metal-oxide-semiconductor (PMOS)metal gates usually changes when the metal gate is subjected to hightemperatures such as is required to activate dopants, replacement gateprocesses have been developed to circumvent the PMOS work functionproblem. In a replacement gate process, transistors are typically firstbuilt in the usual manner using polysilicon gates with silicon dioxidegate dielectric. The polysilion gates and gate dielectric are thenremoved and replaced with high-k gate dielectric and metal gates. A thinsilicon dioxide dielectric is grown on the single crystal silicontransistor channel prior to deposition of the high-k gate dielectric.Because silicide is on the wafer when the thin silicon dioxide is grown,the temperature at which this thin silicon dioxide may be grown islimited. Consequently the thin silicon dioxide dielectric is typicallygrown chemically using SC1 (NH₄OH+H₂O₂). The quality of the silicondioxide dielectric chemically grown may be marginal.

SUMMARY

The following presents a simplified summary in order to provide a basicunderstanding of one or more aspects of the invention. This summary isnot an extensive overview of the invention, and is neither intended toidentify key or critical elements of the invention, nor to delineate thescope thereof. Rather, the primary purpose of the summary is to presentsome concepts of the invention in a simplified form as a prelude to amore detailed description that is presented later.

An integrated circuit and method has a metal gate NMOS transistor with ahigh-k first gate dielectric on a high quality thermally grown interfacedielectric and has a metal gate PMOS transistor with a high-k last gatedielectric on a chemically grown interface dielectric.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1H are illustrations of steps in the fabrication of integratedcircuits formed according to principles of the invention.

FIGS. 2A-2E are illustrations of steps in the fabrication of integratedcircuits formed according to principles of the invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

The present invention is described with reference to the attachedfigures. The figures are not drawn to scale and they are provided merelyto illustrate the invention. Several aspects of the invention aredescribed below with reference to example applications for illustration.It should be understood that numerous specific details, relationships,and methods are set forth to provide an understanding of the invention.One skilled in the relevant art, however, will readily recognize thatthe invention can be practiced without one or more of the specificdetails or with other methods. In other instances, well-known structuresor operations are not shown in detail to avoid obscuring the invention.The present invention is not limited by the illustrated ordering of actsor events, as some acts may occur in different orders and/orconcurrently with other acts or events. Furthermore, not all illustratedacts or events are required to implement a methodology in accordancewith the present invention.

In a typical replacement metal gate transistor flow, NMOS and PMOStransistors with conventional polysilicon gates are formed as usualthrough the silicidation of the source and drains. A premetal dielectric(PMD) is then deposited over these transistors and planarized exposingthe tops of the polysilicon gates. The gates and gate dielectric is thentypically removed and replaced with high-k dielectric and with NMOSmetal gate material with the appropriate NMOS workfunction and PMOSmetal gate material with the appropriate PMOS metal gate workfunction.When the high-k dielectric and the metal gates are deposited after thepolysilicon is removed, the process is termed a high-k last, metal gatelast process flow.

In the embodiment described below, the polysilicon gates are formed onhigh-k dielectric and this high-k dielectric remains in place when theNMOS metal gate material is deposited. The term “high-k first”dielectric indicates the high-k dielectric is deposited before the polygate transistors are formed.

An integrated circuit formed using embodiments of the invention with ann-channel metal-oxide-semiconductor (NMOS) transistor with a gatedielectric stack comprised of a high-k first dielectric 108 deposited ona high quality gate dielectric 106 is shown in FIG. 1H. The embodimentp-channel metal-oxide-semiconductor (PMOS) transistor 132 has a gatedielectric stack comprised of a high-k last dielectric 136 deposited ona second gate dielectric 134. The embodiment process provides a highquality gate oxide 106 for the NMOS transistor 130 while also providinga desirable work function for the PMOS transistor 132. In addition, theembodiment process provides the flexibility of being able toindependently optimize the high-k dielectric 108 for the NMOS and thehigh-k dielectric 136 for PMOS transistors. The higher quality gatedielectric on the NMOS transistor may improve carrier mobility improvingtransistor performance and also may reduce gate current thereby reducingstandby current and prolonging battery life.

The major steps in a process flow illustrating a process for forming anintegrated circuit with an NMOS transistor 130 with a high quality gatedielectric 106 and high-k first gate dielectric 108 and with a PMOStransistor 132 with high-k last gate dielectric 134 is illustrated inFIGS. 1A through 1H.

FIG. 1A is a cross section of a partially processed integrated circuitwith an NMOS transistor 130 with a polysilicon replacement gate 114 andwith a PMOS transistor 132 with a polysilicon replacement gate 116. TheNMOS and PMOS polysilicon replacement gates 114 and 116 are formed on ahigh quality gate dielectric 106 such as silicon dioxide or nitridedsilicon dioxide. A high-k first dielectric such as HfO_(x), HfSiO_(x),HfSiON, ZrO₂, HfZrO_(x), AlO_(x), and TiO_(x) with a thickness in therange of 1 to 4 nm is deposited on the high quality thermally grown gatedielectric 106 using a process such as atomic layer deposition (ALD).(An optional sacrificial layer such as silicon dioxide may be depositedon the high-k first dielectric 108 to protect it during removal of thepolysilicon replacement gate 114). N-type source and drain extensions118 are implanted self-aligned to the NMOS polysilicon replacement gate114. P-type source and drain extensions 120 are implanted self-alignedto the PMOS polysilicon replacement gate 116. N-type deep source anddrain diffusions 124 are implanted self-aligned to the sidewalls 115 onthe NMOS polysilicon replacement gate 114. P-type deep source and draindiffusions 126 are implanted self-aligned to the sidewalls 115 on thePMOS polysilicon replacement gate 116. Premetal dielectric 128 isdeposited over the transistor gates 114 and 116 and planarized usingchemical mechanical polish (CMP) to expose the tops of the NMOS 114 andPMOS 116 polysilicon replacement gates.

The high quality gate dielectric 106 may be SiO₂ grown using insitusteam oxidation (ISSG) to a thickness in the range of 0.5 to 1.5 nm andat a temperature greater than 850° C. Decoupled plasma nitridation (DPN)may be used to convert the surface of the high quality SiO₂ 106 tosilicon oxynitride. In an example embodiment NMOS transistor with highquality thermally grown SiO₂, 0.8 nm ISSG oxide is grown andapproximately 1.5 nm HfO_(x) 108 is deposited on the silicon dioxide 106using ALD.

As shown in FIG. 1B, NMOS transistor photo resist pattern 115 is formedover the NMOS transistor 130 to prevent the NMOS polysilicon replacementgate 114 from being removed. The PMOS polysilicon replacement gate 116is removed by etching to form a PMOS replacement gate transistor trench.The high-k first gate dielectric 108 and high quality gate dielectric108 are etched from the bottom of the PMOS replacement gate transistortrench.

Referring now to FIG. 1C, the photo resist pattern 115 is removed and alow temperature gate dielectric 134 is grown or deposited over thechannel of the PMOS transistor 132. High-k last gate dielectric 136 isthen deposited. The low temperature gate dielectric 134 may be SiO_(x)grown using SC1 wet chemistry. In an example embodiment, approximately0.6 nm SiO_(x) is chemically grown using SC1. The high-k last dielectricmay be a high-k dielectric such as HfO_(x), HfSiO_(x), HfSiON, ZrO₂,HFZrO_(x), AlO_(x), and TiO_(x) in the range of about 1 to 3 nm thick.In an example embodiment approximately 1.5 nm HfO_(x) is deposited usingALD.

As shown in FIG. 1D, PMOS metal gate material 138 is then deposited intothe PMOS replacement gate trench and over the NMOS transistor 130. ThePMOS metal gate material 138 may contain for example, one or more metalsfrom the group consisting of titanium nitride, tantalum nitride,aluminum, and platinum. In an example embodiment the PMOS metal gatematerial 154 is about 8 nm of titanium nitride.

In FIG. 1E PMOS metal gate photo resist pattern 140 is formed on theintegrated circuit to prevent the PMOS metal gate material 138 frombeing removed from the PMOS transistor 132. The PMOS metal gate material138, the high-k last dielectric 136, and the NMOS polysiliconreplacement gate 114 are removed from the NMOS transistor 130 forming aNMOS replacement gate transistor trench. (Prior to removal of the high-klast dielectric an optional sacrificial layer may be removed if it ispresent.)

Referring now to FIG. 1F the photo resist pattern 140 is removed and anNMOS transistor metal gate material 142 is deposited into the NMOStransistor replacement gate trench. The NMOS metal gate material 142 maycontain for example, one or more metals from the group consisting oftitanium, aluminum, titanium-aluminum alloy, and tungsten. In an exampleembodiment the NMOS metal gate material 142 is about 3 nm oftitanium-aluminum alloy.

CMP is used to remove the NMOS metal gate material 142 overfill and thePMOS metal gate material 138 overfill from the surface of the premetaldielectric 128 as shown in FIG. 1G.

As shown in FIG. 1H, a premetal dielectric layer (PMD) 144 may bedeposited and contact plugs 146 may be formed through the PMD 144 layerand through the premetal dielectric layer 128 to affect electricalconnection between the deep source and drain diffusions, 124 and 126,and the first layer of interconnect 148. Additional layers of dielectricand interconnect electrically connected by vias may be formed over thefirst layer of interconnect 148 to complete the integrated circuit.

An alternative embodiment for forming high-k first gate dielectric 108on high quality interfacial dielectric 106 on the NMOS transistor 130and high-k last gate dielectric 134 on a chemically grown interfacialdielectric 134 on the PMOS transistor 132 is illustrated in FIGS. 2Athrough 2F. In this embodiment the process steps prior to FIG. 2A arethe same as the process steps up to and including FIG. 1A.

As shown in FIG. 2A, following the process step described in FIG. 1A,the polysilicon replacement gates, 114 and 116, are removed. The high-kfirst gate dielectric 108 in an example embodiment is HfO_(x) with athickness in the range of 1 nm to 3 nm deposited using ALD and highquality gate dielectric 106 is silicon dioxide grown to a thickness inthe range of 0.5 to 1.5 nm at a temperature greater than 850° C. usingISSG.

In FIG. 2B, an NMOS transistor photo resist pattern 135 is formed on theintegrated circuit with a pattern over the NMOS transistor area 130 toprevent the high-k first gate dielectric 108 and the high quality gatedielectric 106 from being removed from the NMOS transistor 130. An etchwith high selectivity to single crystal silicon is used to remove thehigh-k first gate dielectric 108 and high quality gate dielectric 106from the bottom of the PMOS transistor replacement gate trench.

Referring now to FIG. 2C, the photo resist pattern 135 is removed and alow temperature gate dielectric 134 is grown or deposited over thechannel in the bottom of the PMOS transistor 132 replacement gatetrench. High-k last gate dielectric 136 is then deposited. The high-klast gate dielectric 136 in this embodiment must be able to be removedwith high selectivity from the high-k first gate dielectric 108. Thegate oxide dielectric 134 may be grown using SC1 wet chemistry. In anexample embodiment, approximately 0.6 nm gate oxide 134 is chemicallygrown using SC1. The high-k last gate dielectric may be a high-kdielectric such as HfO_(x), HfSiO_(x), HfSiON, ZrO₂, HFZrO_(x), AlO_(x),and TiO_(x) in the range of about 1 to 2 nm thick. In an exampleembodiment the high-k last gate dielectric 136 is HfSiON with a siliconcontent of about 40% and a thickness in the range of about 1 nm to 3 nmdeposited using ALD. In another example embodiment the high-k last gatedielectric 137 is ZrO₂ with a thickness in the range of about 1 nm to 2nm deposited using ALD.

As shown in FIG. 2D, PMOS metal gate material 138 is then deposited intothe NMOS and PMOS transistor replacement gate trenches. The PMOS metalgate material 138 may contain for example, one or more metals from thegroup consisting of titanium nitride, tantalum nitride, aluminum, andplatinum. In an example embodiment the PMOS metal gate material 138 isabout 8 nm of titanium nitride.

In FIG. 2E PMOS metal gate photo resist pattern 140 is formed on theintegrated circuit to prevent the PMOS metal gate material 138 frombeing removed from the PMOS transistor 132. The PMOS metal gate material138 and the high-k last dielectric 136 are removed from the NMOStransistor 130. In an example embodiment HfSiON high-k last gatedielectric is etched off the HfO_(x) high-k gate first dielectric using1000:1 HF at a temperature of about 80 C. An etch selectivity for HfSiONto HfO_(x) or for ZrO₂ to HfO_(x) of about 20:1 may be attained usingthis etch.

In this example embodiment, subsequent processing after the stepdescribed in FIG. 2D is the same as the process described in stepsillustrated in FIGS. 1F through 1H of the previous embodiment.

Those skilled in the art to which this invention relates will appreciatethat many other embodiments and variations are possible within the scopeof the claimed invention.

What is claimed is:
 1. A process of forming an integrated circuit,comprising the steps: providing a partially processed wafer of theintegrated circuit; growing a high quality first gate dielectric on thepartially processed wafer at a temperature of 850° C. or greater;depositing a high-k first gate dielectric on the high quality first gatedielectric; forming an NMOS polysilicon replacement gate of areplacement gate NMOS transistor on the high-k first gate dielectric;forming a PMOS polysilicon replacement gate of a replacement gate PMOStransistor on the high-k first gate dielectric; depositing a premetaldielectric over the replacement gate NMOS transistor and over thereplacement gate PMOS transistor; planarizing the premetal dielectric toexpose a top of the PMOS polysilicon replacement gate and to expose atop of the NMOS polysilicon replacement gate; forming an NMOS transistorphoto resist pattern wherein the NMOS transistor photo resist patterncovers the NMOS polysilicon replacement gate and exposes the PMOSpolysilicon replacement gate; removing the PMOS polysilicon replacementgate to form a PMOS replacement gate transistor trench; removing thehigh-k first gate dielectric and removing the high quality first gatedielectric from a bottom of the PMOS replacement gate trench; removingthe NMOS transistor photo resist pattern; forming a second gatedielectric layer on the integrated circuit wherein the second gatedielectric covers the bottom of the PMOS replacement gate trench;depositing a high-k last gate dielectric on the integrated circuit;depositing PMOS metal gate material on the high-k last gate dielectric;forming a PMOS transistor photo resist pattern wherein the PMOS photoresist pattern covers the PMOS transistor and exposes the NMOStransistor region; etching the PMOS metal gate material from the NMOStransistor region; etching the high-k last gate dielectric layer fromthe NMOS transistor region; etching the NMOS polysilicon replacementgate to form an NMOS replacement gate transistor trench; removing thePMOS transistor photo resist pattern; depositing NMOS metal gatematerial on the integrated circuit and into the NMOS replacement gatetrench; and polishing the integrated circuit to remove the NMOS and thePMOS metal gate material from a surface of the premetal dielectric andto form an NMOS metal gate in the NMOS replacement gate trench and toform a PMOS metal gate in the PMOS replacement gate trench.
 2. Theprocess of claim 1, wherein the high quality first gate dielectric issilicon dioxide with a thickness in the range of 0.5 to 1.5 nm andwherein the second gate dielectric is SiO_(x) chemically grown with SC1to a thickness of about 0.6 nm.
 3. The integrated circuit of claim 1,wherein the high-k first gate dielectric is selected from the groupconsisting of HfO_(x), HfSiO_(x), HfSiON, ZrO₂, HfZrO_(x), AlO_(x), orTiO_(x) and wherein the high-k last gate dielectric is selected from thegroup consisting of HfO_(x), HfSiO_(x), HfSiON, ZrO₂, HfZrO_(x),AlO_(x), or TiO_(x).
 4. The integrated circuit of claim 1, wherein theNMOS metal gate material is selected from the group consisting oftitanium, aluminum, titanium-aluminum alloy, and tungsten and whereinthe PMOS metal gate material is selected from the group consisting oftitanium nitride, tantalum nitride, aluminum, and platinum.
 5. Theintegrated circuit of claim 1, wherein the high quality gate dielectricis nitrided silicon dioxide with a thickness in the range of about 0.5to 1.5 nm; the high-k first gate dielectric is HfO_(x) with a thicknessin the range of about 1 to 3 nm; the NMOS metal gate material istitanium-aluminum alloy with a thickness of about 3 nm the second gatedielectric layer is chemically grown with SC1 with a thickness of about0.6 nm the high-k last gate dielectric is HfO_(x) with a thickness inthe range of about 1 to 3 nm; and the PMOS metal gate material istitanium nitride with a thickness in the range of about 8 nm.